Manufacture of light concrete



COATING OR PLASTIC.

Patented May 1937 UNITED STATES No Drawing. Application December 31, 1934, In Sweden November 15,

Serial No. 760,018. 1933 3 Claims.

The invention concerns a method of manufacturing a light concrete from Eortland cement aggregates and expansion materials.

A special form of concrete product is the light concrete, a product which is made highly porous by a process creating artificially a high porosity especially by gas development in consequence of a reaction between a suitable metal powder and water. It is possible to reduce in this manner the weight per unit of volume of such concrete products and to increase in this way the heat insulation. A method is already known according to which the concrete is mixed in the usual manner and the mass produced from the prepared mixture of cement and water, possibly with aggregate, is left to indurate in the open air. Besides that it has been already proposed to add finely crushed ashes obtained when burning limestone with bituminous slate as fuel to the cement and to leave this mixture to indurate. According to a thirdproposal a raw mixture is produced from lime, slate ashes and accelerating material, this mixture is then subjected to a process of creating porosity and the finely shaped bodies are steam indurated.

The result-f of all these proposals of manufacturing are unsatisfactory. Although by the process of creating a high porosity it is possible to reduce the weight per unit of volume, all known types of light concrete show a considerable shrinkage, which-strange to say-does not even stop after very long storing, as well as a low strength, crack forming and other disadvantages.

Surprisingly a way has been found which succeeds in avoiding the hitherto known disadvantages and which makes it possible to produce especially a light concrete which shows no shrinkage of practical importance. This material is also distinguished by a high constancy of volume together with a high mechanical strength, and an extraordinary strength against corrosion.

The new method is characterized by the fact that such an amount of very finely divided siliceous material is added to the raw mass e prepared from cement, water aggregates and as I t of generating ex ansion ma erials, that the lime 4 V the cement is completely transformed hm;

fiate'd "monocalcium*'siliat during the steam induration appfied for the Hardening of the conret The induration of the concrete bodies is efiected by means of steam, preferably induration with steam under a pressure of. for instance 5-15 kg./cm. during aperiod of ,5-20 hours.

vfilpecial importance must be laid on the fine PATENT OFFICE grinding of the additional material containing silicic acid if these materials are not finely divided in their natural state. The ilic material should be so finely graded as to pass a sieve of 10,000 meshes per square centimeter, that is 5 about 250 meshes per linear inch. In choosing (j silicic acid material tobe used, raw materials of greatest possible purity are to be preferred. V Especially suitable are g%gqlnd, .ggartgte and the like. The so-ca e puzzo ana suc as trass, slag and the like are less favorable. Relatively e best results were attained up to the present time-using very finely cm shed In this way bodies are produced which have the mudhighest constancy of volume and highest strength together with comparatively low weight.

On the other hand cla especially raw cla is advantageous. Less avorable is clay which has been subjected to a heat treatment such as for instance burnt clay or tile powder.

The proportion of e ad ion of siliceous material is of special importance. I have found that the hardening of cement takes place in a completely different way when steam'is used instead of the customary hardening of the cement in the air. Using steam induration the cement gives rise to calcium silicate with a substantially lower silicic acid content than when the induration of the cement is carried out in the air. Concrete produced from cement, without the addition of very finely crushed silicic acid material by steam induration is substantially lower in quality than such produced from the same materials by induration in the air.

According to experience it seems that the most stable calcium silicic acid composition is the mono-silicate. This silicate is characterized by producing bodies of the highest cubic stability (constancy of volume), the highest mechanical strength as well as the highest resistance against corrosion.

For the use of the silicic acid containing aggregates a very fine crushing is necessary as already mentioned. Here it is recommended to carry out the very fine crushing operation by means of wet grinding, This method furnishes the most suit able product. Apparently the wet crushing increases also the capability of reaction of the silicic acid raw material.

The preparation of the raw mixture can be carried out by way of example in the following manner:

25 parts of of very finely crus ed t are mixed with 25 parts 2% gal and 50 parts material such as s one powder up to 0.5 millimeter size as well as with small quantities o powder. To the mass is then added the necessary amount of water In general this should not amount to less than '70 percent of the cement weight. A higher content of water profinely crushed sand under the same conditions reduces a better texture of the final product and sulted in a compression strength (crushing results also in a saving of the foaming material. strength) of not less than 112 kg./cm.=. This A too high content of water usually does not tremendous difference as to the strength depends weaken the mechanical strength, but increases to upon the fact that the gas expanded or light an undesirable extent the capacity of water abconcrete must have a certain strength before the sorption of the light concrete. steam induration in order to endure the enormous The mass is filled in moulds and then left unheat tensions connected with the steam induratouched 4 to 12 hours. During this time the tion without receiving cracks. These heat tenaluminum powder reacts with the water forming sions can be diminished but never completely hydrogen, the mass increases its bulk, fills'the avoided by using suiilcient preliminary heating. mould completely and even rises above it. After The use of clay as a silicic acid containing ag- 4 to 12 hours the mass rising above the mould gregate is also of certain interest. One reason is cut oil. and the bodies in the mould aresubiectis, because it is an easily accessible material and ed to steam induration under a pressure of for the other reason because the necessary very fine p res pressure above atmoscrushing i. e. the completegrinding canbecarried pheric pfe's'sifre' for Keene-atrabout 10 hours. out technically with comparatively simple means The temperature during the induration should and with low cost. It must be emphasized that, be slowly increased and then be slowly reduced, when using clay, a degree of highest dispersion is because in this manner tensions in the products of special importance. If using 1 it is recomare avoided. mended to use it in a washed state, n which case The use of aggregate is advisable, but not a necessity. If such materials are used, for instance aggregate of the uartzand rock type (in which case in general ma eria s naturally porous are tobe preferred) t e par icles s o d not exgranulated and in this form added to a fresh raw mixture.

The fact that such aggregate finds use in new raw mixtures creates rough outer surfaces of the weight per unit of volume of 0.8 resulted in a compression strength (crushing strength) of 24 lrg./cm. after 12 hours steam induration, whereas a mixture of 50 percent cement and 50 percent suitable electrol es ch as es are used as means or dispersion preliminary 0 he washing.

Using a clay material with 50 percent S10: good results are obtained with mixtures which ried out with tem t 12 atmospheres pressure above atmosp eric. The period of induratio-n amounted to 4-8 hours.

Under certain circumstances it is advisable to contain 20-60-parts cement and 80-40 parts cla ceed0.5 millimeter in diameter lest thinner liquid Working with a mixture of 40 parts cemen and I masses-"set. 60 parts clay resulted for instance in bodies with Asaggregate also, crushed li ht concrete manua weight per unit of volume of 0.7 and a comfactured according to m%tf5n"5an advanpression strength (crushing strength) of 60 jtageously be used 1 coarse crushed form. I kg./cm. Ordinary gas expanded concrete of the 'this case the observance o a cer in size imi same weight showed a compression strength of is not substantially important. Preferably th 1 39 kg./cm.'* after 28 days. It must also be menmaterial rising above the moulds after the treattioned that the light concrete bodies consisting ment of attaining high porosity which is cut oil of clay and cement were practically of constant will be subjected also to the steam induratiom; volume. The induration of the bodies was car- 40 light concrete upon which finishing coats and the like adhere especially well.

For the forming, one uses preferably moulds of considerable dimensions. It is advisable to divide the mass contained in the moulds into formed bodies of desired size immediately before the steam induration. In this way in a single mould for instance 6 to 10 slabs or a corresponding number of large sized blocks can be produced.

The light concrete bodies produced according to the invention show a, shrinkage which per 1 meter length does not exceed 0.1 millimeter. In comparison the shrinkage of the usual gas-expanded concrete amounts to about 3 millimeters per 1 meter length.

If p u re sa nd is used in very finely crushed state as an aggregate it is not difiicult to produce bodies which may show a crushing strength of 150 kg./cm. having a weight per unit of volume of 0.8. It may also be mentioned that weights per unit of volume of 0.2 to 0.3 can be attained with lower strength, but in most cases with sufflcient strength.

. Unexpectedly it has been found that hydraulic binders such as Portland cement give very dif- 0 ierent results fromho'n y rau ic inders such as add one of the usual accelerator m tggifls such as salts, especially chlorides c cium salts soluble glass or on the other Hand organic substances suc as sugar materials or the like may be added to the mixture to be treated. This causes in general an increase of strength without infiuencing the other advantageous qualities of the products according to the invention. ciumchl r in quantities of 2-4 percent referred to the dry weight of cement and of silicic acid containing aggregate produces in general an increase of the compression strength of 25-30 percent. At the same time these materials allow a decrease in the period of induration.

What I claim is:-

1. In, the manufacture of light-weight building material having a low shrinkage, a low hygroscopicity and containing voids of chiefly macroscopic size; the process which comprises mixing together a binder co i in subskantially g1 Portlandcient quantity (:5 o'fiiery finely divided siliceous material to convert substantially all the calcium silicates of higher basicity present into hydrates of mono-calcium silicate, said quantity substantially equaling the weight of the Portland cement present; gas ex- 70 lime because the siliceousmaterial is not of the zolana type, but'cbnsists ofjinburnticljayTfine- -1y crushed sand and similar materials. As an example it can be cited that a mixture of 50 percent lime and 50 percent finely crushed sand with a panding said mixture to produce macroscopic voids and indurating said mixture by steam under sufficient pressure and for a suflicient length of time to produce the said conversion into said hydrates of mono-calcium silicate; said induration being capable of producing substantially the results of an induration for a period of from about 4 to 10 hours at a pressure ranging from about 10 to 12 atmospheres.

2. In the manufacture of light-weight building material having a low shrinkage, a low hygroscopicity and containing voids of chiefly macroscopic size; the process which comprises mixing together a binder consisting substantially of Portland cement, gas expanding materials, aggregate, water and a sufiicient quantity of finely divided siliceous material to convert substantially all silicates of higher basicity into hydrates of mono-calcium silicate, said siliceous material substantially equalling the weight of the Portland cement present and having a fineness of the order of 250 mesh; introducing such mixture into a mold before expansion has taken place, gas expanding said mixture to produce macroscopic voids while in said mold, removing any excess material from said mold, and indurating said mixture by steam under sufiicient pressure and- 

